I recently came back to Slime Rancher after a few months hiatus, and I noticed that my vacpack can only hold 50 units in each slot. I'm level 24 in the 7Zee Rewards Club, and it shows that the "Tank Booster Ultra" is sold out on the vacpack upgrades. I specifically remember having the ability to hold 100 units in each slot a few months ago, but it seems to have disappeared now that I've returned.

Is there any way to get this upgrade back? It's super frustrating playing in the late game with only 50 unit slots!